1. Field of the Invention
The subject invention relates to devices for filling implantable medication devices and, more particularly, to devices for providing a flow of liquid through the septum of a medication vial at atmospheric pressure.
2. Description of the Prior Art
The prior art includes types of implantable medication infusion devices designed to deliver medication at a selected rate. Generally, these devices have included a reservoir storing a supply of medication that would permit continued operation of the device over an extended period before the supply had to be replenished.
In many prior art infusion devices, the reservoir was refillable by access through a septum that could be penetrated by a hypodermic needle. Typically, the needle was to be pushed through the septum and the medication injected under pressure into the reservoir. When the reservoir was filled, the needle was withdrawn. Examples are shown in U.S. Pat. Nos. 3,951,147; 4,221,219; 4,229,220; and 4,360,019 as well as U.S. patent application Ser. No. 439,138 filed Nov. 11, 1981 by Robert E. Fischell.
Early infusion devices were basically pressurized reservoirs from which the medication was to be controllably gated into a catheter. Examples are shown in U.S. Pat. Nos. 4,193,397; 4,221,219; 3,731,681; 4,299,220; 3,894,538; and 3,951,147. The reservoirs of these devices were generally filled by a pressurized flow from a hypodermic needle and syringe. Other filling devices such as shown in U.S. Pat. No. 4,190,048 were also known.
One disadvantage of such pressurized reservoir devices was that, in certain failure modes,they could potentially discharge uncontrolled amounts of medication into the patient's body. Moreover, it was recognized that, in using a refill device such as a syringe that provided pressurized flow, a potential also existed that the fill needle might not be correctly placed through the septum. In that event, the medication could inadvertently be injected into the patient's body instead of the reservoir.
In later injection devices, it was recognized that a device that could maintain the medication in a reservoir having an absolute pressure slightly below atmospheric pressure would be inherently safer since the potential for discharging uncontrolled amounts of medication from the reservoir in certain failure modes did not exist. Examples of these devices are shown in U.S. Pat. Nos. 4,360,019, 4,373,527 and 4,525,165.
More recently, such below-atmospheric pressure infusion devices have incorporated an antechamber that is located between the septum and the reservoir. A poppet valve that cooperates with the septum to form the antechamber is in a normally closed position to seal off the reservoir and permit the medication therein to be maintained at below-atmospheric pressure. The poppet valve is forced open by the fill needle when it is inserted through the septum into the antechamber. This provides a flow path through the septum and into the reservoir. Thus, medication supplied through the fill needle at atmospheric pressure will flow through the antechamber and into the reservoir. Unless the fill needle is properly inserted through the septum and into the antechamber to open the poppet valve, the fill needle is not in communication with the reservoir. Under those conditions, there is no pressure differential to cause flow out of the needle. Thus, this arrangement avoids the possibility that the medication will inadvertently be injected directly into the body. An example of this type of system is shown in U.S. Pat. No. 4,573,994.
While such below-atmospheric pressure infusion devices afforded many advantages, a disadvantage was that the medication had to be actively pumped out of the reservoir. In certain devices, air that was entrained or dissolved in the fluid system could form a bubble inside the chamber of the pump. Because of the relatively high elasticity of air, there was a potential in these devices for air bubbles to compromise their efficiency as well as the accuracy of the medication dosages that they delivered.
Typically in the prior art, such below-atmospheric pressure devices were filled by use of a device that was vented to atmospheric pressure. These devices required that the medication first be removed from the commercial vial in which it was received from the manufacturer and then placed in another container such as a hypodermic syringe. The syringe or other container was then vented to atmospheric pressure. The structure of such devices typically provided cavities and chambers where air could be entrapped and ultimately carried into the infusion device. As previously explained, this could compromise the performance of the infusion device. Moreover, by requiring that the medication first be transferred from the vial to another container, these devices not only provided an additional step at which air could be introduced to the medication, but also barred any effective use of the medication directly from the vial.
Accordingly, there was a need for an improved filling device that could provide a safe flow of medication at atmospheric pressure, that did not contain pockets or cavities tending to introduce air into the fluid delivered to the reservoir and that would provide for the use of medication directly from the vial, thus allowing the use of medication that was deaerated in the vial by the pharmaceutical manufacturer.